The convenience and flexibility offered by radio frequency identification (RFID) techniques have caused this technology to become popular in recent years. Specifically, RFID technology facilitates contactless communication of personal and commercial information. For example, use of an RFID tag in a retail or logistical context allows a customer to select a basket of goods and bring those goods to a supermarket exit, without having to engage in time consuming bar code scanning: The RFID tag on the product allows the information list of the goods to appear on a screen, and then the customer can provide payment for those goods. With use of an RF interrogator, an RFID tag, an antenna, and a manage block, such an RFID system transforms the formerly cumbersome and lengthy payment procedure an easy and quick one. Moreover, RFID technology allows a merchant to automatically update product inventories in real time. Numerous other possible applications exist for RFID technology apart from the retail environment just described.
One key step in the application of RFID technology is the demodulation of a signal received as a result of RF interrogation of the RFID tag. Typical digital data modulation procedures between interrogator and transponder in RFID systems include amplitude shift keying (ASK), frequency shift keying (FSK), and phase shift PSK (phase shift keying), with ASK being most commonly used.
A couple of approaches have conventionally been used to demodulate an ASK signal. In coherent detection, a local coherent reference is multiplied with the received signal. A filter is then used to obtain the approximate envelope of the signal. The original signal can then be recovered utilizing a sample-and-hold circuit with a threshold device.
Noncoherent detection is a second approach conventionally employed to demodulate an ASK signal. In noncoherent detection, the signal envelope is first extracted, and then a sample-and-hold circuit plus a threshold device are used to recover the original signal.
Demodulation of ASK signals by coherent detection offers excellent performance, but requires relatively complex and expensive structures for the implementation. By contrast, demodulation of ASK signals by noncoherent detection requires simpler and cheaper structures. This approach, however, offers good performance only where the incoming received signal exhibits a large signal to noise ratio. Despite this limitation, because cost considerations typically predominate in the mass production of consumable electronic products, noncoherent detection has thus far been the preferred approach for ASK demodulation.
From the above, it is seen that an improved technique for demodulating ASK signals is desired.